Vascular aneurysms are the result of abnormal dilation of a blood vessel, usually from disease or a genetic predisposition, which can weaken the arterial wall and allow it to expand. Aneurysms can occur in any blood vessel, but most occur in the aorta and peripheral arteries, with the majority of aneurysms occurring in the abdominal aorta. An aneurysm is at risk of rupture resulting in extravasation of blood into, for example, the peritoneal cavity or into tissue surrounding the diseased artery.
Aneurysms, especially abdominal aortic aneurysms, are commonly treated in open surgery procedures in which the diseased vessel segment is bypassed and repaired with an artificial vascular graft. While open surgery is an effective surgical technique in light of the risk of a fatal abdominal aortic aneurysm rupture, the open surgical technique suffers from a number of disadvantages. The surgical procedure is complex, requires a long hospital stay, requires a long recovery time, and has a high mortality rate. Less invasive devices and techniques have been developed to avoid these disadvantages.
In particular, aneurysm exclusion devices, such as endoluminal vascular prostheses and stent grafts, may be positioned and deployed within the affected artery through insertion catheters by percutaneous procedures in a less or minimally invasive procedure than open surgical procedures. The tubular endoluminal prosthesis is introduced in a small diameter crimped condition and expanded at the aneurysm. Aneurysm exclusion devices are used to exclude vascular aneurysms and provide a prosthetic lumen for the flow of blood. Although often referred to as stent grafts, these tubular endoluminal prostheses differ from covered stents in that they are not used to mechanically prop open natural blood vessels. Rather, they are used to secure an artificial lumen in a sealing engagement with the vessel wall without further opening the abnormally dilated natural blood vessel.
Stent grafts for use in aneurysms typically include a support structure supporting a woven graft material. Examples of textile graft materials are woven, braided, or knitted polymer or metallic materials, e.g., polyester, polytetrafluoroethylene, polypropylene, stainless steel, or nitinol. The graft material is secured to the inner or outer diameter of the support structure, which supports the graft material and/or holds it in place against a luminal wall. The stent graft is generally secured to a vessel wall above and below the aneurysm. A proximal spring stent of the stent graft can be located above the aneurysm to provide a radial force which engages the lumen wall and seals the stent graft at the lumen wall.
As noted above, the graft material in a conventional stent graft is commonly a woven textile structure. Weaving involves the interlacing of two sets of threads or yarns at right angles to each other: the warp or end yarns and the weft, fill or pick yarns. The warp yarns are held taut and in parallel order, typically by means of a loom. The loom is warped (or dressed) with the warp yarns passing through heddles on two or more harnesses. The warp yarns are moved up or down by the harnesses creating a space called the shed. The weft yarns are inserted into the shed at an angle perpendicular to the warp yarns in a process called filling. There are different types of filling mechanisms, including, for example and not by way of limitation, shuttles, rapiers, and projectiles. There are different types of weaves, including, for example and not by way of limitation, plain weaves, twill weaves, and satin weaves.
Textile structures or patterns are distinguished from other structures by the manner in which they are made. For example, a braided structure or pattern is formed by intertwining three or more strands of flexible material such as textile fibers or yarns. Compared to the process of weaving a wide sheet of cloth from two separate, perpendicular groups of strands (warp and weft), a braid is usually long and narrow, with each component strand functionally equivalent in zigzagging forward through the overlapping mass of the others.
As shown in FIGS. 1-2, a conventional stent graft 100 includes a graft material 102. Graft material 102 is generally a woven textile product, constructed in a tubular configuration, by means of a shuttle loom, resulting in end or warp yarns 104 that run longitudinally and parallel to longitudinal axis 110 and fill or weft yarns 106 that run circumferentially. Braided textile materials are generally not suitable for stent grafts because braided materials tend to be unstable and generally too porous due to the lack of interaction between yarns. However, conventional stent grafts 100 with stent graft material 102 having warp yarns 104 running longitudinally and weft yarns 106 running circumferentially may lack flexibility in certain performance characteristics.
Accordingly, a woven graft material and method of forming an endovascular prosthesis using such a woven graft material that permits improved performance characteristics the prosthesis is needed.